1. Field of the Invention
The present invention relates to a link mechanism and is applicable to a blowing mode switching device in a vehicle air-conditioning apparatus.
2. Description of the Related Art
In a conventional vehicle air-conditioning apparatus, a door (damper) means is operated to control the conditioned air flow through a link mechanism including a plurality of link levers (see for example Japanese Patent Laid-Open Publication No. Sho 63-297854).
FIG. 6 is a view of a test model link mechanism developed by the inventor. In the link mechanism, a grooved portion 22a provided at a second link lever 22 is open at an end and a cam 23 in contact with the second pin 21b of a first link lever 21 is not provided with a guide wall to restrict the first link lever 21 from swinging in such a direction that the second pin 21b moves away from the cam surface 23a of the cam 23. Therefore, when the first link lever 21 rotates excessively to the left (counter-clockwise), the first pin 21a of the first link lever 21 could come out of the grooved portion 22a. 
The disadvantage may be solved by forming the grooved portion of the second link lever 22 into a closed shape or providing the guide wall to the cam 23. However, if the grooved portion 22a has a closed end, the second link lever 22 can be increased in size, while the guide wall provided at the cam 23 may interfere with other elements.